Recently, the market of imaging apparatuses such as digital cameras have been very large and there have been a wide variety of user demands for imaging apparatuses of digital cameras etc. Not only demands for the higher image quality and the smaller and thinner body, but also demands for the higher magnification and the wider angle of imaging units including zoom lenses have been recently very great.
Generally, a positive lead-type optical system with a lens group closest to an object having positive refractive power has an advantage that its scaling factor is made larger, and is often used as a type suitable for higher magnification at the scaling ratio exceeding five times, for example.
Specifically, as a small positive lead-type optical system, an optical system (zoom lens) having a four-group configuration of four lens groups having positive, negative, positive, positive refractive power sequentially from the object side toward an image side has been known (for example, see Patent Document 1 (JP-A-2006-23529), Patent Document 2 (JP-A-2005-338740), Patent Document 3 (Japanese Patent No. 3977150), and Patent Document 4 (JP-A-2006-308957)).